At present, aluminium electrolytic industry still employs a conventional Hall-Heroult process; electrolyte always takes cryolite-aluminium oxide as a basic system, and the cryolite generally adopts sodium fluoroaluminate. As the aluminium electrolysis process progresses, the sodium fluoroaluminate and aluminium oxide are continuously consumed; therefore, in order to ensure the continuous progressing of aluminium electrolysis, it is necessary to supplement electrolyte and aluminium oxide to the electrolyte basic system respectively. The existing electrolyte supplement system mainly includes aluminium fluoride and sodium fluoroaluminate; the electrolytic temperature needs to be maintained at about 960 DEG C. in the entire aluminium electrolysis process and thus power consumption is high, this is mainly because the liquidus temperature of the electrolyte is high and it is necessary to keep a certain temperature of superheat degree to make the aluminium oxide have a better solubility.
The method for preparing cryolite in industry generally adopts a synthesis method, in which anhydrous hydrofluoric acid reacts with aluminium hydroxide to form fluoaluminic acid; then the fluoaluminic acid reacts with sodium hydroxide or potassium hydroxide at a high temperature; after processes of filtering, drying, melting and crushing, the cryolite is prepared, wherein the cryolite synthesized by this method has a molecular ratio of m=3.0, with a relatively high melting point. The cryolite synthesized by the existing industrial synthesis method has a molecular ratio of m=2.0˜3.0, and it is difficult to obtain the relatively pure low-molecular-ratio cryolite with a molecular ratio of m=1.0˜1.5.
Therefore, the conventional art has disadvantages that the electrolytic power consumption is high and the electrolyte supplement system is not ideal.